After breaking his leg and piling on 50lbs, John Smith took Vyvanse to suppress his ap­petite. This was on the advice of a medical-student friend who had lost a “near-miraculous” 20lbs despite no change to his lifestyle. Vyvanse did the trick: Mr Smith swiftly shed the excess weight.

However, he also noticed that when he used Vyvanse, a prescription drug to treat binge-eating and attention deficit hyperactivity disorder (ADHD) in children and adults, he could “hyper-focus” on his work. Now the 30-year-old (who chose a pseudonym when interviewed for this article) “pops a small dose” every time he needs to power through his work as an analyst for an investment group in the US.

Michael Craig is a consultant psychiatrist at the London-based Nightingale and Maudsley hospitals and works with adults with ADHD. He has encountered patients with no medical need demanding pills. One mother of a teenager preparing to study in the US was particularly aggressive in her demands for a prescription. “She felt that it wasn’t a level playing field if her child was not using them.”